1. Field of the Invention
The present invention relates generally to methods for altering gene expression in a cell or animal using viral constructs engineered to deliver an RNA molecule, and more specifically to deliver double-stranded RNA molecules that can be used to down-regulate or modulate gene expression. Particular aspects of the invention relate to down-regulating a pathogenic virus gene or a gene necessary for a pathogenic virus life cycle through delivery of a viral construct engineered to express an RNA molecule. In some embodiments, the RNA molecule is not toxic to a target cell.
2. Description of the Related Art
RNA interference (RNAi) or silencing is a recently discovered phenomenon (A. Fire et al., Nature 391, 806 (1998); C. E. Rocheleau et al. Cell 90, 707 (1997)). Small interfering RNAs (“siRNAs”) are double-stranded RNA molecules that inhibit the expression of a gene with which they share homology. siRNAs have been used as a tool to down regulate the expression of specific genes in a variety of cultured cells as well as in invertebrate animals. A number of such approaches have been reviewed recently (P. D. Zamore, Science 296, 1265 (2002)); however, such approaches have limitations. For example, no technique prior to the invention described herein allows for the generation of transgenic mammals having a specific gene down regulated through RNA interference. Similarly, there is a need for more robust methods for the introduction of small RNA molecules with regulatory function. The invention provided herein addresses these and other limitations in the field of RNA mediated gene regulation. Likewise, there is a need for improved methods and compositions for the treatment of viruses and diseases associated with viral infection.
Cytotoxicity and other adverse effects of small RNA molecules in target cells have been noted in the art and correlated with expression levels of the siRNA (D. S. An et al., Mol. Ther. 14, 494-504 (2006)). Utilizing weaker promoters to express the small RNA molecules has been shown to reduce apparent toxicities; however, the potency of the siRNAs was also attenuated.
Studies have reported adverse effects such as, for example, induction of interferon response genes (see R. J. Fish and E. K. Kruithof, BMC. Mol. Biol. 5, 9 (2004)), global change of mRNA expression profiles caused by off target effects (see A. L. Jackson et al., RNA. 12, 1179-1187 (2006)) and cytotoxic effects due to microRNA dysregulation (D. Grimm et al., Nature. 441, 537-541 (2006)). Cytotoxic effects have also been observed in in vitro cultured human T lymphocytes upon shRNA expression (D. S. An et al., Mol. Ther. 14, 494-504 (2006)). Any cytotoxic effects of siRNA could be particularly problematic in situations where siRNA expression is to be maintained in a living organism stably over long-term, for example, in order to achieve intra-cellular immunization against HIV-1 disease (D. Baltimore, Nature 335, 395-396 (1988)).